There are computer systems in which an operator interacts with the system by touching or pointing to various positions within a touch screen area. The touch screen serves as easily used data input apparatus because the operator can quickly and easily feed data into a computer by indicating various specific positions of the touch screen area.
The term "pointer" as used herein means a stylus, rod, dowel, finger, pencil, or similar relatively long and slim element which is readily movable by hand and which is easily oriented generally perpendicular to a two-dimensional plane surface or area in space or in the air and is easily moved relative to the area while being held in such a generally perpendicular orientation.
As used herein, the term "touch screen" (whether singular or plural) means apparatus used to locate the position of a pointer oriented generally perpendicular to a two-dimensional plane. In accordance with the present invention, such a two-dimensional plane may be an area defined on or near the surface of solid material, such as near an inert panel, or may be a geometric plane defined in space or in the air.
Such "touch screens" have many possible applications, for example: pointing to or selecting a particular image or region on a video screen or on a panel, plate or tablet to select or indicate a specific item, informational element, letter, number, symbol, parameter line, region or characteristic; to locate or track a pointer held generally perpendicular to the plane and moved along the plane for plotting data, drawing a graph or picture or for laying out a network or diagram; for indicating or tracking the relative motion or coordinates of movement or trajectory of a moving object; for use as a custom keyboard in an electronic input module; and so forth.
Existing touch screens in use today suffer from a number of problems or shortcomings.
An optical touch screen system uses numerous light-emitting diodes (LED's) arranged along two adjacent borders of a rectangular area for emitting crossed beams of infrared radiation traversing the touch screen area, and numerous photodetectors arranged along the other two borders for sensing these beams. These systems are adversely affected by ambient light which can cause misreadings of the photodetectors. The numerous LED's and detectors involve maintenance problems, because they become coated by dust or dirt and must be cleaned carefully and are subject to misalignment if the mounting frame is significantly bumped or jarred. These optical systems provide only a medium resolution, typically providing only 40 by 27 individually responsive spots, a total of about 1,080 respective spots. They evidence a relatively large parallax when used in front of a video screen, because the infrared beams are spaced relatively far away from the face of the video screen, with the parallax problem being most apparent near the corners of the video screen. The reliability of optical touch screen systems is only fair, due to the fact that the beams are so very easily accidentally interrupted, for example, by a dropped object or sheet of paper, thereby feeding false and confusing data into the system.
Acoustic surface touch screen systems typically provide only medium resolution of 40 by 27 individually responsive spots, the same order of resolution as for optical systems discussed above. These systems involve numerous piezoelectric transducers arranged along two borders of a vibratable glass surface for generating acoustic waves which ripple over the glass surface and are reflected in an echo pattern from the touched spot. These acoustic systems tend to be unreliable, because the acoustically vibrating glass surface is extremely sensitive and easily causes misreadings due to dirt or small scratches on the vibrating glass surface which create spurious echoes. Parallax of acoustic surface touch screens is a major drawback due to the thickness of the vibrating glass thereby offsetting the touch sensitive areas spaced relatively far from the face of a video screen.
Capacity sensing touch screen systems provide a relatively low resolution because they involve relatively large touch sensitive regions, for example, each such region may measure about 1/2 square inch in area. This very low resolution with such relatively large area individual touch sensitive regions considerably limits the applications and uses for which capacitance touch screens can be employed. A capacitive-type touch screen system is the most durable and reliable of the presently commercially available systems, but its resolution is very low as already pointed out. Capacitive touch screens are adversely affected by temperature and humidity fluctuations.
Resistance membrane touch screen systems offer the highest resolution now commercially available. Numerous fine parallel resistive electrodes are etched onto the surfaces of two mylar plastic sheets with these electrodes on the two sheets being oriented at right angles to each other in a sandwich. Numerous voltage-drop sensors arranged along two edges of this sandwich with associated measuring circuits including analogue to digital converters are needed to sense and to locate the touched spot. Depending upon the cost and complexity of such a system resolution can range from 256 by 256 pixels up to 4,000 by 4,000 pixels. The pair of etched mylar plastic membranes which are used in these resistance membrane systems are very delicate and very easily damaged. When used on the face of a video screen such resistance membranes have been known to slide slightly from their original locations, thereby creating parallax errors. Their optical transmission attenuation and dispersion due to their etched surfaces cause reduced visibility and clarity of video images as seen through these etched membranes. Also, the characteristics of the exposed parallel resistance electrodes on the membrane surfaces change with humidity. Thus, the resistance membrane screen must be relinearized each time that the system is turned on.
Transparent membrane (X Y Switch Matrix) systems offer relatively high resolution, typically providing 64 by 64 touch responsive points, thus giving an overall total of 4,000 touch points. These systems include two closely spaced but normally separated layers of optical grade polyester film each having a set of parallel electrically conductive flexible electrodes. The sets of electrodes in the two spaced polyester sheets are oriented at right angles to each other, and there are numerous digital switches. A digital switch is connected to each electrode. Sufficient force must be exerted against a touch point on the upper (or outer) polyester sheet to deflect that local area of electrodes on the upper sheet into contact with an electrode on the lower sheet for ativating the respective digital switches for the X and Y coordinates. The X Y Switch Matrix touch screen systems are expensive, and the upper (or outer) polyester sheet is exposed and subject to damage from excessive deflection pressures or sharp pointers.
The various touch screen systems as discussed above employ five types of existing technology. Each system involves a relatively large number of components, and thus considerable assembly time is needed in manufacturing any of these prior systems. Their costs are relatively high in proportion to the total numbers of touch responsive areas which are provided.
Also, any given prior art touch screen system is inherently fixed in size. Once the numerous detectors, LED's, transducers, capacitance elements, resistive elements, analogue to digital converters, contact electrodes, digital switches, etc. have been arrayed, the touch screen size is confined and limited to that particular size of the array.